class Solution {
public:
    string maximumTime(string time) {
        if(time[0] == '?'){
            if(time[1] == '?' || time[1] < '4')time[0] = '2';
            else time[0] = '1'; 
        }
        if(time[1] == '?'){
            if(time[0] == '2')time[1] = '3';
            else time[1] = '9'; 
        }
        if(time[3] == '?')time[3] = '5';
        if(time[4] == '?')time[4] = '9';
        return time;
    }
};

//2021.7.24 
